These Dulce de Leche Swirle Tarts are as delicious as they are beautiful. Dulce de Leche is mixed with white and dark to create gorgeous multi-colored swirls. Note: this recipe makes 4 six-inch tarts which can typically serve 8.
Combine the flour, cocoa powder, sugar, and salt in the bowl of a food processor, and pulse briefly until everything is well-blended. Add the cold cubed butter and pulse until it is in small pea-sized pieces. Add the egg yolk and pulse in 5-second bursts until the dough starts clumping together.
Turn it out of the food processor and knead it lightly several times to incorporate any extra flour and cocoa powder. At this point, the dough can be wrapped and refrigerated for several days. If you’re ready to use it now, spray four 6-inch removable bottom tart pans with nonstick cooking spray. Press the dough into the bottom and sides of the pans in a thin, even layer.
Freeze the shells for 30 minutes, and while they’re in the freezer, preheat the oven to 375 degrees F. Spray the tops of the tart dough with nonstick spray, then press a sheet of foil into the shells and fill the foil with dry beans, rice, or pie weights. Bake the shells for 10-12 minutes, then carefully remove the foil and weights. Bake for an additional 7-8 minutes to fully bake the shells, until puffed, dry, and fragrant. Let the shells cool completely before filling them.
To Make the Dulce de Leche Filling:
Remove the paper wrapper from the can of condensed milk. Place it in a slow cooker then fill it with water that comes an inch above the can. Set the slow cooker to low heat, cover it, and leave it to cook for 8-9 hours. (This can be done overnight, so that you wake up to dulce de leche!) Once cooked, carefully remove the can from the water and let it cool completely before proceeding.
Place the finely chopped white chocolate in a medium bowl. Pour 1/2 cup of heavy cream into a small saucepan and bring it to a simmer over medium-high heat. Pour the hot cream over the chopped white chocolate, and let it sit for 1 minute to soften the chocolate. After a minute, gently whisk the white chocolate and cream together until it is smooth and silky. If chunks of white chocolate remain, microwave the bowl in 10-second increments, whisking well after each one, until they are entirely melted. Finally, add the room temperature butter and salt and whisk them in.
Separate out 1/2 cup of the white chocolate filling into a small bowl and set aside. To the remaining white chocolate, add the dulce de leche and whisk it in until smooth.
Separate out 1/2 cup of the dulce de leche filling. Melt the semi-sweet chocolate in a small bowl, then mix the melted chocolate into the 1/2 c of dulce de leche. Add the remaining 2 tbsp of cream to thin out the chocolate mixture, if needed. You should now have a small bowl of chocolate dulce de leche filling, a small bowl of white chocolate filling, and a larger bowl of dulce de leche filling.
Spoon the dulce de leche filling into the cooled tart shells, filling them about half full. Take a small spoon and dollop small spoonfuls of the 3 different fillings on top of a tart in a random pattern. Take a toothpick and swirl it through the filling to create a marbled pattern. Repeat with the remaining tarts. Depending on the height of your tart shells, you may be left with some excess filling. It is delicious on cookies, crackers, toast, or your fingers!
Refrigerate the tarts until the filling is set, for about 1 hour. The tarts can be made in advance and kept in an airtight container in the refrigerator for 3-4 days. For the best taste and texture, let them sit at room temperature for about 30 minutes before serving, so the filling is soft and silky.
For this recipe, you will want to use dulce de leche that has a very thick texture, like peanut butter. Runny, liquid dulce de leche will make your tart filling too loose. The recipe below uses my favorite method for making dulce de leche, and there are a few alternative methods listed in the note at the bottom. Note that making dulce de leche will take hours, so ideally you should make it the day before you assemble the tarts. Store-bought dulce de leche can be used, provided it has the right texture. If you don't have a slow cooker, you can also make dulce de leche on the stovetop. Place the can of condensed milk in a deep saucepan, and fill the pan with water so that the can is completely submerged. Bring the water to a simmer and allow it to simmer for 5 hours. Several times an hour, check the saucepan to make sure that the water is still covering the top of the can, and add water as necessary. After 5 hours, remove the can and let it cool completely before using it. This crust recipe was adapted from Dorie Greenspan's excellent book Baking: From My Home to Yours.